In Kitchen, we see grief presented in a couple of different ways. After Eriko's death, Yuichi retreats and doesn't share his grief or emotions with anyone. Satsuki, on the other hand, tries to remain in contact with friends and family after the death of her boyfriend, Hitoshi, because she doesn't want to be alone with her thoughts. Like Yuichi, she doesn't discuss her grief much.
Within the Japanese culture, death is often dealt with by first making arrangements, whether they are following Shinto or Buddhist rituals. Like in Kitchen, the grieving process of the Japanese is often very slow. There tends to be an emphasis on grieving together as a group. We see this very little in the book, other than offers for company and providing food. However, Mikage and Yuichi help one another through their grieving processes in this manner and thus might be considered a group of two.